The weak safety culture of a now-defunct railway company and poor government oversight contributed to an oil train explosion that killed 47 people in Quebec in 2013, Canadian authorities have announced in their report on the disaster.

The Transportation Safety Board chairwoman, Wendy Tadros, said 18 factors played a role, including a rail company that cut corners and a Canadian regulator that did not do proper safety audits.

The safety board issued its report 13 months after a runaway train carrying 72 carloads of volatile oil from North Dakota derailed, hurtled down an incline and slammed into downtown Lac-Megantic, Quebec. Several train cars exploded and 40 buildings were levelled. The unattended train had been parked overnight on a rail line before it came loose. The safety board said its brakes were not properly set by the engineer.

Montreal, Maine & Atlantic Railways went bankrupt after the disaster. Three of its employees have been charged by Quebec prosecutors with 47 counts of criminal negligence causing death. Class action lawsuits are pending.

Investigators blamed another government agency, Transport Canada, for failing in its oversight duties. “Transport Canada didn’t audit railways often enough and thoroughly enough to know how those companies were really managing, or not managing, risk,” Tadros said.

The Canadian transport minister, Lisa Raitt, said she had directed Transport Canada to take concrete action based on the TSB recommendations.

Tadros said Transport Canada knew Montreal, Maine & Atlantic Railways was having problems but there was no proper follow-up.

TSB chief operating officer Jean Laporte called Montreal, Maine & Atlantic’s operations “dubious” and said the railway chose to limit the speed on certain routes instead of improving its equipment. “People only did the bare minimum to get the job done rather than always following the rules,” Laporte said.

The crash, the worst railway accident in Canada in nearly 150 years, prompted intense public pressure to make oil trains safer. Canada’s transport minister said in April that the type of tankers involved in the disaster must be retired or retrofitted within three years because they were prone to rupturing.

The oil industry has rapidly moved to using trains to transport oil in part because of oil booms in North Dakota’s Bakken region and Alberta’s oil sands, and because of a lack of pipelines.

The Lac-Megantic disaster along with a string of other explosive accidents across North America prompted the US Department of Transportation to issue an alert about the potential high volatility of crude from the Bakken oil patch. The US agency said that light crude oil from the Bakken region, which straddles North Dakota, Saskatchewan and Manitoba, may be different from traditional heavy crudes because it is prone to ignite at a lower temperature.

Edward Burkhardt, the Montreal, Maine and Atlantic Canada chairman who became the target of the community’s anger last year, said he could not comment on the report because of pending legal cases.

John Giles, chief executive of Central Maine and Quebec Railway, which purchased the assets of Montreal, Maine and Atlantic Canada, said better safety practices had been put in place including the elimination of one-man crews, the hiring of a senior superintendent for Canadian operations, the swapping out of old locomotives. The railroad was spending $8.5m on overhauling neglected track and would delay any crude oil shipments until 2016, he said.